It is known to provide the treads of the tires with tread patterns formed of a plurality of blocks delimited by grooves of generally transverse and circumferential (or longitudinal) orientation. Each block of the tread pattern has a so-called leading face and a trailing face, each of which faces intersects the contact face of the block to form an edge (leading edge and trailing edge, respectively). The leading edge corresponds to a line of points of the contact face coming first as the tire contacts the road.
Trailing edges of blocks in the patterns tend to wear to a greater extent than leading edges which are brought into contact with a road surface earlier than the trailing edges, to thus produce uneven wear of the blocks in the patterns. Such a peculiar wear is referred to as “heel-and-tow wear”.
Another problem commonly encountered by all types of tire treads is that of stone trapping. If a stone or a piece of gravel or a like object is of similar or slightly larger size to a groove between blocks in the tire tread, it is very likely that stones or like objects lodge in the groove. As the tire rotates the stone or the like object rubs against the groove boundary and can cause damage. The likelihood of damage is even greater when the stone or like object contacts the groove base since a tear can start from this location. If a stone does lodge in a groove and can be prevented from contacting the groove base the possibility of a tear being caused is substantially reduced.
EP 393,873 discloses a vehicle tyre having a tread surface of ribs, blocks or pads and substantially U- or V-shaped tread grooves arranged therebetween wherein at least one of the two sidewalls of at least a part of the tread grooves is provided with grip enhancing steps which extend in the longitudinal groove direction and follow the sidewall contour. A pronounced improvement is achieved in traction, in particular on snow.
U.S. Pat. No. 4,423,760 discloses a tire tread for a truck tire comprising a small number of circumferential zig-zag grooves, wherein the sidewalls of each groove are each provided with a supporting buttress of varying height or width such that the maximum support is provided at or adjacent the points where the groove projects into the surrounding tread rubber. The provision of such a buttress provides a varying degree of support for each groove sidewall along the length of the groove and assists in preventing uneven wear of the tread rubber and reduces damage caused by stones trapped in the groove.